Inkjet printing devices generate printed text and images by firing ink droplets at print media. Generally, a movable printhead carries an array of nozzles that fire the ink droplets on command from selected nozzles within the array. The quality of the resulting printed output can depend on the ability of the nozzles to fire droplets of consistent size along defined, reproducible trajectories to the print media.
Individual nozzles within the array may malfunction during their use. For example, during and after printing operations, ink residues tend to accumulate within and around nozzle orifices. These residues may prevent nozzle firing, may cause nozzles to fire droplets along undesired trajectories, and/or may cause droplets to have inconsistent sizes. Accordingly, printheads and their nozzles should be serviced to avoid malfunctioning that degrades printing device performance.
Inkjet printing devices may include a structure, termed a service station, for performing maintenance operations that reduce problems with printhead function, specifically nozzle firing. The service station may include and/or accommodates capping, wiping, and spitting operations. Capping operations hermetically seal nozzles between print jobs to reduce ink evaporation from nozzles. By contrast, wiping and spitting operations may be used both between and within print jobs to wipe away, eject, and/or dissolve ink residues, to reduce the incidence and severity of nozzle malfunctioning.
One or more of these maintenance operations may be initiated by positioning a printhead in a service portion of a printing device, and then moving an appropriate functional region of the service station to the printhead. Accordingly, the service station may be mounted on a movable sled that reciprocates to position the appropriate functional regions of the service station adjacent to, or in contact with, the printhead. For example, the service station may include a wiper mechanism having wipers that are pulled across the surface of a stationary printhead to remove accumulated residue. However, implementation of the wiper mechanism and other service station operations may reduce printing throughput and also may reduce printhead longevity. Therefore, inkjet printing devices may include detection mechanisms to measure the fidelity of ink droplet delivery, in order to coordinate selective implementation of service station mechanisms or operations. Such detection mechanisms also may be useful for defining corrective firing algorithms, for example, when malfunctioning nozzles cannot be serviced effectively.
Detection mechanisms for measuring droplet trajectories in inkjet printing devices may use contact between ink droplets and a substrate, such as a detector or print media, to define ink droplet positions and thus measure trajectories. Mechanisms based on contact may require that the substrate be cleaned regularly to remove deposited ink. Such cleaning may be time-consuming and may damage the substrate, for example, when a detector acts as the substrate. Alternatively, the substrate may be replaced after its use by the detection mechanism. However, replacing the substrate is wasteful and requires the substrate to be replenished.